1. Field of the Invention
The present invention relates to a laminated ceramic electronic component and a method for manufacturing the laminated ceramic electronic component, and more particularly, to a laminated ceramic electronic component, for example, including a conductor film that defines an external terminal electrode, which is directly formed by plating so as to be electrically connected to a plurality of internal conductors, and a method for manufacturing the laminated ceramic electronic component.
2. Description of the Related Art
As shown in FIG. 7, a laminated ceramic electronic component 101 typified by a laminated ceramic capacitor typically includes a component main body 105 which has a stack structure including a plurality of stacked ceramic layers 102 composed of, for example, a dielectric ceramic, and a plurality of internal electrodes 103 and 104 formed along the interfaces between the ceramic layers 102. The plurality of internal electrodes 103 and the plurality of internal electrodes 104 each have ends respectively exposed at two opposite end surfaces 106 and 107 of the component main body 105, and external terminal electrodes 108 and 109 are formed respectively so as to electrically connect the respective exposed ends of the internal electrodes 103 to each other and electrically connect the respective exposed ends of the internal electrodes 104 to each other.
For the formation of the external terminal electrodes 108 and 109, typically, a metal paste containing a metal constituent and a glass constituent is applied onto the end surfaces 106 and 107 of the component main body 105, and then subjected to firing, thereby forming paste electrode layers 110 first. Next, a first plating layer 111 containing, for example, nickel as its main constituent is formed on the paste electrode layers 110, and a second plating layer 112 containing, for example, tin or gold as its main constituent is further formed thereon. More specifically, the external terminal electrodes 108 and 109 are each composed of a three-layer structure of the paste electrode layer 110, the first plating layer 111, and the second plating layer 112.
The external terminal electrodes 108 and 109 are required to provide favorable solderability when the laminated ceramic electronic component 101 is mounted onto a substrate with the use of solder. At the same time, the external terminal electrode 108 is required to serve to electrically connect the plurality of internal electrodes 103 to each other, which are electrically insulated from each other, and the external terminal electrode 109 is required to serve to electrically connect the plurality of internal electrodes 104 to each other, which are electrically insulated from each other. The second plating layer 112 described above serves to ensure solderability, whereas the paste electrode layer 110 serves to electrically connect the internal electrodes 103 to each other and the internal electrodes 104 to each other. The first plating layer 111 serves to prevent solder erosion in solder joint.
However, the paste electrode layer 110 has a large thickness of several tens μm to several hundreds μm. Therefore, in order to limit the dimensions of the laminated ceramic electronic component 101 up to certain specifications, there is undesirably a need to reduce the effective volume for ensuring a capacitance, because there is a need to ensure the volume for the paste electrode layers 110.
On the other hand, the plating layers 111 and 112 each have a thickness on the order of several μm. Thus, if the external terminal electrodes 108 and 109 can be composed of only plating films such as the first plating layer 111 and the second plating layer 112, the effective volume can be ensured more for ensuring the capacitance, and the effective volume fraction can be thus improved. However, when plating is applied directly onto the end surfaces 106 and 107 of the component main body 105, the following problems may be encountered.
First, as shown in FIG. 8, a component main body 122 of a laminated ceramic electronic component is supposed to have a rectangular parallelepiped shape including an LW surface 123 defined by a length dimension L and a width dimension W, an LT surface 124 defined by the length dimension L and a thickness dimension T, and a WT surface 125 defined by the width dimension W and the thickness dimension T, and have a plurality of ceramic layers 126 extending in the direction of the LW surface 123, which are stacked in the thickness direction. It is to be noted that the end surfaces 106 and 107 of the component main body 105 shown in FIG. 7 correspond to the WT surface 125.
To take a laminated ceramic capacitor as an example of the laminated ceramic electronic component, the laminated ceramic capacitor includes, as in the case of sections indicated by a dashed line in FIG. 8, outer layer sections 129 extending along the LW surface 123 and width-direction gap sections 130 along extending the LT surface 124 as protective sections, outside an effective section 128 which has a plurality of internal electrodes 127 distributed therein and forms a capacitance.
When a plating film is to be formed on the WT surface 125, it is only for the region corresponding to the effective section 128 that a sufficient coverage with the plating film can be achieved while controlling plating deposition appropriately. Therefore, the ingress of moisture, etc., is highly likely to be caused along the interface between the plating film and the component main body 122 from an end edge of the plating film, and in addition, the fixing strength of the plating film tends to be decreased. On the other hand, in the case of setting up such a condition that can increase the degree of growth of the plating film, it is difficult to control the degree of the plating growth, and there will be thus great variability caused in the film formation region.
It is to be noted that if the region on which a plating film is to be formed is subjected to a pretreatment such as a catalytic treatment, the problems as described above can be solved to some extent. However, the pretreatment such as a catalytic treatment to only a specific point is complicated, which is not preferable.
Therefore, for example, the technique disclosed in Japanese Patent Application Laid-Open No. 2004-146401 or Japanese Patent Application Laid-Open No. 2004-40084 has been attracting attention.
Japanese Patent Application Laid-Open No. 2004-146401 discloses a method in which a conductive paste or a conductive resin is applied onto at least ridge sections of end surfaces of a component main body along the direction of stacking internal electrodes so as to come into contact with leading sections of the internal electrodes, and the conductive paste is subjected to firing or the conductive resin is thermally cured to form a conductive film, and further, the end surfaces of the component main body are subjected to electroplating, thereby forming an electroplating film so as to be connected to the conductive film on the ridge sections described above. This method ensures that a plating film can be formed so as to reach and cover the conductive film on the ridge sections.
On the other hand, Japanese Patent Application Laid-Open No. 2004-40084 discloses, in particular, in FIG. 8B, etc. thereof, an internal anchor tab formed as a dummy internal electrode in an outer layer section, and a plating film formed so as to reach at least an exposed end of the internal anchor tab.
However, in the method described in Japanese Patent Application Laid-Open No. 2004-146401, when the conductive films formed on the ridge sections of the end surfaces of the component main body are formed by firing of the conductive paste, the glass contained in the conductive paste then makes it more likely to be dissolved in a plating solution, thereby permitting the ingress of moisture to be caused. On the other hand, in the case of using the conductive resin, the conductive resin has the drawback of weakness to the heat treatment, and seems to have poor fixing strength.
Next, the technique described in Japanese Patent Application Laid-Open No. 2004-40084 allows the plating film to extend even to the outer layer section, with the use of the WT-surface exposed end of the internal anchor tab placed in the outer layer section as a nucleus for plating deposition, but fails to allow the plating film to extend onto the width-direction gap section, thus permitting the ingress of moisture to be caused therefrom.